Lesson Overview

1. Lesson Overview 26.3 Primate Evolution

2. THINK ABOUT IT • Primates means “first” in Latin. But what are primates “first” in? • When primates appeared, there was little to distinguish them from other mammals. As primates evolved, however, several characteristics became distinctive.

3. What Is a Primate? • What characteristics do all primates share?

4. What Is a Primate? • What characteristics do all primates share? • In general, a primate is a mammal that has relatively long fingers and toes with nails instead of claws, arms that can rotate around shoulder joints, a strong clavicle, binocular vision, and a well-developed cerebrum.

5. What Is a Primate? • Primates share several adaptations for a life spent in trees. • In general, a primate is a mammal that has relatively long fingers and toes with nails instead of claws, arms that can rotate around shoulder joints, a strong clavicle, binocular vision, and a well-developed cerebrum. • You can see most of these characteristics in a lemur.

6. Fingers, Toes, and Shoulders • Primates typically have five flexible fingers and toes on each hand or foot that can grip objects firmly and precisely, enabling many primates to run along tree limbs and swing from branches with ease.

7. Fingers, Toes, and Shoulders • Most primates have thumbs and big toes that can move against the other digits, allowing them to hold objects firmly in their hands or feet.

8. Fingers, Toes, and Shoulders • Primates’ arms can rotate in broad circles around a strong shoulder joint attached to a strong clavicle, or collar bone, making them well suited for climbing.

9. Binocular Vision • Many primates have forward-facing eyes, giving them excellent binocular vision. • Binocular vision is the ability to combine visual images from both eyes, providing depth perception and a three-dimensional view of the world. • This comes in handy for judging the locations of tree branches, from which many primates, like this lemur, swing.

10. Well-Developed Cerebrum • In primates, the “thinking” part of the brain—the cerebrum—is large and intricate, which enables more-complex behaviors than are found in many other mammals. • For example, many primate species create elaborate social systems that include extended families, adoption of orphans, and even warfare between rival troops.

11. Evolution of Primates • What are the major evolutionary groups of primates?

12. Evolution of Primates • What are the major evolutionary groups of primates? • Primates in one of these groups look very little like typical monkeys. This group contains the lemurs and lorises. The other group includes tarsiers and the anthropoids, the group that includes monkeys, great apes, and humans.

13. Evolution of Primates • Humans and other primates evolved from a common ancestor that lived more than 65 million years ago.

14. Evolution of Primates: • Early in their history, primates split into two groups.

15. Evolution of Primates • Primates in one of these groups look very little like typical monkeys. This group contains the lemurs and lorises.

16. Evolution of Primates: • The other group includes tarsiers and the anthropoids

17. Lemurs and Lorises • Lemurs and lorises are small, nocturnal primates with large eyes adapted to seeing in the dark. Many have long snouts. • Living members include the bush babies of Africa, the lemurs of Madagascar, and the lorises of Asia.

18. Tarsiers and Anthropoids • Anthropoids, or humanlike primates, include monkeys, great apes, and humans.

19. Tarsiers and Anthropoids • Anthropoids split into two groups around 45 million years ago, as the continents on which they lived moved apart.

20. New World Monkeys • The New World monkeys are found in Central and South America. • Members of this group live almost entirely in trees. They have long, flexible arms that enable them to swing from branches. • New World monkeys also have a long, prehensile tail that can coil tightly enough around a branch to serve as a “fifth hand.”

21. Old World Monkeys and Great Apes • The other anthropoid branch, which evolved in Africa and Asia, includes the Old World monkeys and great apes. • Old World monkeys spend time in trees but lack prehensile tails.

22. Old World Monkeys and Great Apes • Great apes, also called hominoids, include gibbons, orangutans, gorillas, chimpanzees, and humans. • Recent DNA analyses confirm that, among the great apes, chimpanzees are humans’ closest relatives.

23. Hominine Evolution • What adaptations enabled later hominine species to walk upright?

24. Hominine Evolution • What adaptations enabled later hominine species to walk upright? • The skull, neck, spinal column, hip bones, and leg bones of early hominine species changed shape in ways that enabled later species to walk upright.

25. Hominine Evolution • Between 6 and 7 million years ago, the lineage that led to humans split from the lineage that led to chimpanzees. • The hominoids in the lineage that led to humans are called hominines and include modern humans and all other species more closely related to us than to chimpanzees.

26. Hominine Evolution • Hominines evolved the ability to walk upright, grasping thumbs, and large brains. • The skull, neck, spinal column, hip bones, and leg bones of early hominine species changed shape in ways that enabled later species to walk upright.

27. Hominine Evolution • This figureshows some ways in which the skeletons of modern humans differ from those of hominoids such as gorillas.

28. Hominine Evolution • The evolution of bipedal, or two-footed, locomotion was very important, because it freed both hands to use tools. • The hominine hand evolved an opposable thumb that could touch the tips of the fingers, enabling the grasping of objects and the use of tools.

29. Hominine Evolution • Hominines evolved much larger brains. • Most of the difference in brain size results from an expanded cerebrum, which is, as you recall, the “thinking” part of the brain.

30. New Findings and New Questions • The study of human ancestors is exciting and constantly changing. • Recent discoveries in Africa have doubled the number of known hominine species and the length of the known hominine fossil record. • These data have enhanced the picture of our species’ past, but questions still remain as to how fossil hominines are related to one another—and to humans.

31. Relatives Versus Ancestors • The hominine fossil record includes seven genera—Sahelanthropus, Orrorin, Ardipithecus, Australopithecus, Paranthropus, Kenyanthropus, and Homo—and at least 20 species. • All these species are relatives of modern humans, but not all of them are human ancestors.

32. Relatives Versus Ancestors

33. The Oldest Hominine? • In 2002, paleontologists in Africa discovered a fossil skull roughly 7 million years old. This fossil, called Sahelanthropus, is a million years older than any known hominine.

34. The Oldest Hominine? • Sahelanthropus had a brain about the size of a modern chimp, but its short, broad face was more like that of a human. • Scientists are still debating whether this fossil represents a hominine.

35. Australopithecus • Hominines of the genus Australopithecus lived from about 4 million to about 1.5 million years ago. Australopithecus afarensis fossils are shown. • These hominines were bipedal apes, but their skeletons suggest that they probably spent some time in trees. • The structure of their teeth suggests a diet rich in fruit.

36. Australopithecus • Australopithecus afarensis fossils indicate the species had small brains. Excavations have found fossilized humanlike footprints that were probably made by members of A. afarensis about 3.6 million years ago. Such finds show that homines walked bipedally before large brains evolved.

37. Australopithecus • Other A. afarensis fossils indicate that males were much larger than females.

38. Lucy • The best-known A. afarensis specimen is a partial skeleton of an adult female discovered in 1974, nicknamed “Lucy.” • Lucy stood about 1 meter tall and lived about 3.2 million years ago.

39. The Dikika Baby • In 2006, an Ethiopian researcher announced the discovery of some 3.3 million-year-old fossils of a very young A. afarensis female, nicknamed “the Dikika Baby.” • The skeleton included a nearly full skull and jaws, torso, spinal column, limbs, and left foot. • Leg bones confirmed that the Dikika Baby walked bipedally, while her arm and shoulder bones suggest that she would have been a better climber than modern humans.

40. Paranthropus • The more-recent Paranthropus species had huge, grinding back teeth, and their diets probably included coarse and fibrous plant foods like those eaten by modern gorillas.

41. Paleontologists place Paranthropus on a separate, dead-end branch of our family tree.

42. Hominine Relationships • A series of hominine adaptive radiations produced a number of species whose relationships are difficult to determine. • As a result, what once looked like a simple hominine “family tree” with a single main trunk now looks more like a shrub with multiple trunks.

43. The Road to Modern Humans • What is the current scientific thinking about the genus Homo?

44. The Road to Modern Humans • What is the current scientific thinking about the genus Homo? • If you look at the Hominine Time Line, you can see that many species in our genus existed before our species, Homo sapiens, appeared. Furthermore, at least three other Homo species existed at the same time as early humans.

45. Many species in our genus existed before our species, Homo sapiens, appeared.

46. At least three other Homo species existed at the same time as early humans.

47. The Genus Homo: About 2 million years ago, a new group of hominine species appeared.

48. The Genus Homo • The fossils of this new group of hominine species resemble modern human bones, and so they are classified in the genus Homo. • One set of fossils was found with tools made of stone and bone, so it was named Homo habilis, which means “handy man” in Latin.

49. The Genus Homo • The earliest fossils that researchers assign to the genus Homo belong to Homo ergaster.

50. The Genus Homo • H. ergaster was larger than H. habilis and had a bigger brain and downward-facing nostrils that resemble those of modern humans.